In a process for removing material from a bore in a workpiece, the typical assembly to perform such a material removal process includes an elongate support member (e.g., an elongate boring bar) wherein one end of the boring bar connects to a cutting head which carries a cutting insert and the other end of the boring bar attaches to a support member. In order to accomplish the material removal operation, the cutting head extends into the bore of the workpiece so that the relative rotation between the cutting insert (held by the cutting head) and the workpiece enables the cutting insert to contact the surface which forms the bore, and hence, remove material (e.g., form a circumferential groove) from the surface of the bore.
Because of the fact that the boring bar has a cutting head at the one end thereof and the other end thereof attaches to a support member, the boring bar has a cantilever relationship with the support structure. Because of the nature of the cantilever relationship, the boring bar experiences certain stresses and strains during the material removal operation so that in order to provide adequate support to the cutting head and cutting insert held thereby, the boring bar should possess a relatively high modulus of elasticity and a relatively high degree of stiffness.
Heretofore, boring bars have been made from steel, hard metal (e.g., tungsten carbide), and tungsten alloys. While boring bars made of tungsten carbide have possessed a high modulus of elasticity and a sufficiently high stiffness, the brittleness of the tungsten carbide has resulted in these boring bars experiencing early failures. While the steel boring bars and the tungsten alloy boring bars may not possess the brittleness of the tungsten carbide, the stresses and strains which these boring bars experience can exceed the elastic limit of the material. The consequence of which is the permanent deformation of these boring bars which leads to a reduction in the useful life thereof.
It is apparent that there exists a need to provide a boring bar which possesses sufficient rigidity and resistance to plastic deformation so as to not deform under working conditions, and yet, is not so brittle as to fail in a premature fashion.
In the manufacture of tungsten carbide boring bars, as well as in the manufacture of tungsten alloy boring bars, sintering is the typical process by which the material is consolidated to form the boring bar. It can sometimes occur that as a result of the sintering process, the boring bar experiences warpage (or curving). This is an undesirable result since the extent of warpage may so great as to cause the boring bar to be unfit for use. While the warpage may not be so great as to cause the boring bar to be scrapped, the absence of optimum straightness in the boring bar may reduce the useful life of the boring bar and may also negatively impact upon the quality of the material removal operation.
It is apparent that it would be beneficial to provide a boring bar made via a sintering process wherein the finished boring bar would possess an optimum degree of straightness. By providing a boring bar with an optimum degree of straightness, the number of boring bars that would have to be scrapped would be diminished and the number of boring bar that would have a shortened useful life or would not provide for the optimum removal of material would be reduced.
In some circumstances, the boring bar must exhibit a certain degree of smoothness so as to not exceed a certain degree of surface roughness. It is not unusual that a sintered boring bar may undergo a post-sinter material removal treatment so as to create a surface with the requisite smoothness. It would be desirable to provide a process for making a sintered boring bar wherein the as-sintered boring bar has the requisite surface roughness, and hence, does not have to undergo a post-sinter material removal treatment.
In one form thereof, the invention is an elongate support member which comprises a body which has an exterior surface, an exterior region adjacent to the exterior surface thereof and an interior region remote from the exterior surface. The interior region is contiguous with the exterior region so as to define an interface therebetween. The interior region is of a first hardness. A portion of the exterior region adjacent to the exterior surface is of a second hardness. The second hardness is greater than the first hardness.
In another form thereof, the invention is a process for making an elongate support member comprising the steps of: providing an elongate body with a transverse dimension and a longitudinal dimension, and the body has a pre-swaged exterior surface and a pre-swaged interior region; swaging the body so as to reduce the transverse dimension of the body and increase the longitudinal dimension of the body so to form a post-swaged exterior surface, an exterior region, and a post-swaged interior region wherein the exterior region is mediate of a post-swaged exterior surface and the post-swaged interior region; the post-swaged interior region being of a first hardness; a portion of the exterior region adjacent to the post-swaged exterior surface being of a second hardness; and the second hardness being greater than the first hardness.
In still another form thereof, the invention is a cutting assembly that comprises a cutting insert, and a cutting head carrying the cutting insert. The assembly further includes a support holder, and an elongate support member wherein the support member has opposite ends wherein one of the ends attaches to the cutting head and the other end connects to the support holder. The support member has an exterior surface, an exterior region adjacent to the exterior surface thereof, and an interior region remote from the exterior surface. The interior region is contiguous with the exterior region so as to define an interface therebetween. The interior region is of a first hardness. A portion of the exterior region adjacent to the exterior surface is of a second hardness. The second hardness is greater than the first hardness.